Be sure to fill the lowest energy levels first (Aufbau principle) when using the diagram
above. In filling orbitals having equal energy, electrons are added to the orbitals to half fill them
all before any pairing occurs (Hund’s rule). Sometimes it is difficult to remember the relative
energy position of the orbitals. Notice that the 4s fills before the 3d. Figure 5.2 may help you
remember the pattern in filling. Study the pattern and be able to reproduce it during the exam.
Basics 491 s2 s3 s4 s5 s6 s7 s2 p3 p4 p5 p6 p7 p3 d4 d5 d4 f5 f6 dFigure 5.2 Orbital filling pattern.5p4p3p2p4d3d5s4s3s2s1s↑↑↓↑↓↑↓↑↓↑↓↑↓↑Figure 5.3 Energy-level diagram for silicon.Following these rules, the energy-level diagram for silicon (Z = 14) can be written as shown
in Figure 5.3